This invention relates to the scrubbing of exhaust gas stream and, more particularly, to the scrubbing of highly reactive gases from exhaust streams emanating from semiconductor device processing.
The semiconductor industry relies on the use of a wide range of thermal, chemical and plasma driven processes to produce semiconductor devices on silicon and other substrates. Such processes generally involve both the deposition of material on to and the removal of material from the substrates and structures on the surface.
Much of the equipment used for these processes requires vacuum pumps to control the environment within a process chamber during operation of the processes. Many of the chemicals used in these fabrication processes are extremely corrosive and chemically reactive and form undesirable by-products which can be harmful to the environment if released and can lead to a breakdown of the vacuum pumps and other equipment used for controlling the operation of the processes.
For example, many semiconductor processes involve the use of highly reactive gases such as silane (SiH.sub.4), ammonia (NH.sub.3), phosphine (PH.sub.3), diborane (B.sub.2 H.sub.6) and tetraethylorthosilicate (TEOS). Such gases have to be pumped from the process chamber at the relevant part of the semiconductor processing to the atmosphere and if they decompose in the vacuum pump could lead to pump failure. In any event, the gases themselves or their reaction products should not be released into the atmosphere.
Numerous previous processes and apparatus have been proposed for scrubbing such exhaust gas streams from semiconductor processing. These prior processes include a variety of wet chemical processes in which one or more noxious species in an exhaust stream can be rendered harmless; they also include different dry processes including those described in Patent Specification No WO 89/11905 in which such noxious species can be reacted in, for example, a two stage heated dry scrubber comprising a silicon granule first stage and a calcium oxide second stage, both stages being conveniently held in a stainless steel tube.
In addition, certain types of combustion chamber processes have been proposed, particularly ones involving the combustion of the exhaust stream gases mixed with fuel gas and oxygen in a combustion system, for example one having a foraminous burner.
Although some of these prior processes/apparatus have met with commercial success, there remains a need for alternative systems to deal with certain types of exhaust stream components and, in particular, one which could be operated at low pressures to enable them to scrub the exhaust stream components prior to the stream entering the vacuum exhaust system or, alternatively, between the stages of a multistage vacuum pump or between two separate vacuum pumps.